1. Field of the Invention
The present invention relates to a medium provided with a magnetic body and a magnetic body sensing device, and particularly, to a medium provided with a magnetic body and a magnetic body sensing device that senses the medium in a non-contact manner, and prevents erroneous sensing that may occur when the magnetic body sensing device performs sensing of the medium along some directions, thereby to improve the accuracy of sensing.
2. Description of the Related Art
Various methods and devices for enhancing security have been proposed. Such methods and devices are designed to prevent leaks of confidential or personal information, or prevent forgery of securities or the like by unauthorized copying.
For the purpose of preventing forgery of securities or the like, a method has been proposed in which securities or the like are made of a special paper having therein a latent image formed in a specific pattern or formed with special ink containing an infrared absorbing agent, for example.
In this method, when securities made of such a special paper is copied with a scanner (image input device) or copying machine, a latent image of a specific pattern or a latent image drawn with special ink formed in the special paper is printed in a visually observable state. With the printed latent image, the fact that the securities were copied is recognized, thereby enabling to prevent the forgery of securities.
It is known to provide a forgery preventing paper and securities made of such paper, which make it very difficult to forge securities by the use of a color copying machine and to forge the paper itself for the securities. This forgery preventing paper is manufactured by mixing, in a paper base material consisting of pulp fibers, small pieces of paper or fiber fibrils coated with an ink containing a metameric pigment with substantially the same amount of small pieces of paper or fiber fibrils colored with an ordinary color ink which looks the same hue as that of the ink containing the metameric pigment under ordinary light such as sunlight, whereby when a document such as securities made of the forgery preventing paper is copied, two kinds of spots with differing hues appear on the color-copied paper and thus the forgery of securities can be prevented.
It is also known to provide an image processing device and a method of adding a specific pattern when a specific original document is copied. According to this technique, the specific property of an original document is determined by comparing an image from the original document with an image from a transferred material. An output image from the original document with such specific property is always processed before outputting the same, so that if a specific original document (e.g. banknote) that is supposed not to be copied is copied, a clue is provided for locating the copying machine used for the unauthorized copying.
However, the techniques disclosed above require special operations such as scanning image data of an original document, transferred material, or securities. It has therefore been desired a method, device or forgery preventing paper, which, without performing such special operations, is capable of protecting securities against fraudulent copying, or determining whether or not a specific original document.
Further, it is known to provide a robbery preventing label (tag) used in an electronic article surveillance (EAS) system. According to this technique, a robbery preventing label is provided with a soft magnetic thin film used as an active element. The robbery preventing label is designed to be usable in an electronic article inspection system without being affect by orientation of the label at the detector outlet of the system. Specifically, the soft magnetic thin film has an easy magnetization axis in a specific direction, and the robbery preventing label is folded along at least one folding line, so that the robbery preventing label has at least two layers which overlap at least partially with each other, at least one of the folding lines intersects with the direction of the easy magnetization axis to form an oblique angle, and thus the direction of the easy magnetization axis of one of the layers differ from the directions of the easy magnetization axes of other layers.
However, this robbery preventing label is designed such that a response signal from the robbery preventing label can be detected at a predetermine level irrespective of orientations of the magnetic field and the robbery preventing label by differing the direction of the easy magnetization axis of one layer from the directions of the easy magnetization axes of the other layers. Thus, a method of applying this robbery preventing label to a medium to enable unique identification of the medium and sensing and identifying a desired medium from plural media provided with such robbery preventing label is not disclosed.
Further, it is known to provide a magnetic marker that is readable in a non-contact manner and has various information recorded in a magnetic pattern and a method of reading such a magnetic marker. According to this technique, the magnetic marker is provided with a magnetic pattern such that the easy magnetization direction forms a predetermined angle with a scanning direction, and encoding is thus performed with an angle formed between the easy magnetization direction and the scanning direction. As the results, it is made possible not only to read the magnetic marker in a non-contact manner but also to represent analog data or multi-value data by the use of a single bar.
However, this magnetic marker is designed such that encoding is performed by using an angle formed between the easy magnetization direction of the magnetic pattern and a scanning direction. Therefore, if a medium provided with the magnetic marker is placed in an arbitrary orientation, an angle formed between the easy magnetization direction of the magnetic pattern and a scanning direction will vary, even for the same medium, according to the orientation where the medium is placed, and a sensed code will possibly be detected as a different code.